Molecular genetic basis of pod corn ( Tunicate maize)

Abstract

Pod corn is a classic morphological mutant of maize in which the mature kernels of the cob are covered by glumes, in contrast to generally grown maize varieties in which kernels are naked. Pod corn, known since pre-Columbian times, is the result of a dominant gain-of-function mutation at the Tunicate ( Tu ) locus. Some classic articles of 20th century maize genetics reported that the mutant Tu locus is complex, but molecular details remained elusive. Here, we show that pod corn is caused by a cis -regulatory mutation and duplication of the ZMM19 MADS-box gene. Although the WT locus contains a single-copy gene that is expressed in vegetative organs only, mutation and duplication of ZMM19 in Tu lead to ectopic expression of the gene in the inflorescences, thus conferring vegetative traits to reproductive organs.

TAWAWA1 , a regulator of rice inflorescence architecture, functions through the suppression of meristem phase transition

“…These results support the hypothesis that SVP genes function downstream of TAW1. Interestingly, the ectopic expression of SVP genes in barley and maize also resulted in the severe suppression of SM identity, suggesting that SVP function might be conserved among grasses (34)(35)(36). In conclusion, our data indicate that TAW1 suppresses the acquisition of SM identity through the induction of SVP genes, which consequently promote or prolong BM identity.…”

Pod Corn Is Caused by Rearrangement at the Tunicate1 Locus

“…Previously, genomic cloning recovered two Zmm19 genes in Tu1, known as Tu1-A and Tu1-B, and one gene each in Tu1-d, Tu1-l, and Tu1-md (Munster et al, 2004;Wingen et al, 2012). Sequence analysis indicated that both Tu1-l and Tu1-d were analogous to Tu1-B, whereas Tu1-md was analogous to Tu1-A.…”

“…This analysis revealed that both Tu1-A and Tu1-B are structurally rearranged by insertion of a novel 2-kb Mu-like element in the 59 cis-regulatory region of Zmm19, which is fused with the 39 flanking region of an unknown gene (GRMZM2G006297) located on the other side of the 1.8-Mb interval from Zmm19 in the opposite orientation ( Figure 2B). This 1.8-Mb chromosomal inversion would be expected to inhibit recombination and likely accounts for the cold spot ( Figure 2A) that prohibited previous attempts to precisely map Zmm19 relative to Tu1 (Münster et al, 2002;He et al, 2004;Wingen et al, 2012). The analyses also revealed that Tu1-A is distinguished from Tu1-B by the presence of a 3.5-kb insertion in the first intron, a non-long terminal repeat retrotransposon ( Figure 2B, yellow triangle).…”

“…A MADS box gene in maize, Z. mays MADS19 (Zmm19), lies in the same genetic interval as Tu1 (Münster et al, 2002;He et al, 2004). Furthermore, ectopic expression of Zmm19 results in leaflike sepals in Arabidopsis thaliana, resembling the elongated glumes in Tu1 mutants (He et al, 2004;Wingen et al, 2012). Zmm19 is misexpressed in the inflorescence of Tu1 mutants, and two duplicated copies of the gene were found in Tu1, but only one copy was found in Tu1-l, Tu1-d, and Tu1-md (He et al, 2004;Wingen et al, 2012).…”

“…Furthermore, ectopic expression of Zmm19 results in leaflike sepals in Arabidopsis thaliana, resembling the elongated glumes in Tu1 mutants (He et al, 2004;Wingen et al, 2012). Zmm19 is misexpressed in the inflorescence of Tu1 mutants, and two duplicated copies of the gene were found in Tu1, but only one copy was found in Tu1-l, Tu1-d, and Tu1-md (He et al, 2004;Wingen et al, 2012). Despite these promising indications, genome sequencing has revealed several other candidate genes in the same interval (Schnable et al, 2009).…”